Color sensors are used for color detection, color measurement, and color control in both open and closed loop systems. Typical color sensors convert the primary color components of light, namely red (R), green (G), and blue (B) to analog voltage outputs. FIG. 1 depicts an example of a color sensor 10 that includes a sensor module 12 and a post-sensor amplification unit 14. The sensor module includes R, G, and B bandpass filters 16, 18, and 20 and a photodetector array 22 with individual photodetectors 24, 26, and 28 that are aligned with the color filters to provide color-specific responses. In operation, light 30 is incident on the color filters of the sensor module. Separate portions of the light are filtered by the respective R, G, and B color filters and the filtered light is detected by the corresponding photodetectors. The photocurrent generated by the different photodetectors in response to the filtered light is amplified by amplifiers 30 of the post-sensor amplification unit. Color-specific output voltages (Vred, Vgreen, and Vblue) are generated in response to the amplification.
Although color sensors as described with reference to FIG. 1 work well, the signals that are output from the amplifiers tend to be skewed by offset voltages at the input terminals of the amplifiers. If not corrected, the offset voltages will negatively impact the performance of the color sensor. Additionally, offset voltages tend to vary in a random nature, which complicates any attempt to correct for the offset.
In view of this, what is needed is a color sensing technique that addresses the offset voltage problem and that is efficient to implement.